1. Programming Abstractions Cynthia Lee CS106B

2. Today’s Topics ADTs  Map › Example: counting words in text  Containers within containers › Example: reference tests › Example: anagram finder (Friday)

3. Maps What are they?

4. Associative containers Map Set Lexicon Not as concerned with order but with matching  Set: associates keys with membership (yes or no)  Map: associates keys with values (could be any type) set "the" "of" "from" "to" "she" "you" "him" "why" "in" "down" "by" "if" "Cynthia" "Mehran" "Marty" "497-3070" "555-0000" "867-5309" map

5. Stanford library Map (selected member functions) template class Map { public: void add(const KeyType& key, const ValueType& value); bool containsKey(const KeyType& key) const; ValueType get(const KeyType& key) const; ValueType operator [](const KeyType& key) const;... }  Map phone;// Map takes *two* template parameters  phone["Cynthia"] = "497-3070";// two options for add syntax  phone.add("Mehran", "867-5309"); // two options for add syntax  cout << phone["Cynthia"] << endl; // two options for get syntax  cout << phone.get("Mehran") << endl; // two options for get syntax

6. Map programming exercise Write a program to count the number of occurrences of each unique word in a text file (e.g. Poker by Zora Neale Hurston).  First do an initial report: › Print all words that appeared in the book at least 10 times, in alphabetical order  Then go into interactive query mode: › The user types a word and we report how many times that word appeared in the book (repeat in a loop until quit). 6

7. Map programming exercise Write a program to count the number of occurrences of each unique word in a text file (e.g. Poker by Zora Neale Hurston).  The user types a word and we report how many times that word appeared in the book (repeat in a loop until quit). What would be a good design for this problem? A.Map wordCounts; B.Map > wordCounts; C.Map wordCounts; D.Map > wordCounts; E.Other/none/more 7

8. Write a program to count the number of occurrences of each unique word in a text file (e.g. Poker by Zora Neale Hurston). 8 Map wordCounts; string word; infile >> word; while (!infile.fail()) { //record count here infile >> word; } How can we record the count? A.wordCounts[word] += word; B.wordCounts[word] += 1; C.wordCounts[word]++; D.B and C are good, but you need to first detect new (never seen before) words so you can start at zero before you start adding +1 E.Other/none/more

9. Write a program to count the number of occurrences of each unique word in a text file (e.g. Poker by Zora Neale Hurston).  Report all words that appeared in the book at least 10 times, in alphabetical order 9 Does this work for our alphabetical use case?  Yes!  Stanford library Map returns its keys in sorted order cout << "Most common words:" << endl; for (string word : wordCounts){ if (wordCounts[word] >= 10){ cout << word << "\t"; cout << wordCounts[word] << endl; } New (C++11) useful tool! for loop that iterates over all elements of a container class